Military


HAVE BLUE Flight Test Program

In 1975, both Lockheed and Northrop were awarded Phase 1 contracts for 4-month projects that would conclude with model tests and selection of one firm for a Phase 2 award. Both presented concepts that were predicted to meet or exceed the signature goals. Early in Phase 1, the program was classified "Top Secret." Lockheed and Northrop were to construct one-third and full-scale pole models, which were then tested on a radar range to see which company best met DARPA's criteria for a high-stealth aircraft. Lockheed Skunk Works engineers determined that an airplane with faceted surfaces could have a remarkably low radar signature because the surfaces would radiate 99.9 percent of the radar energy away from the receiver.

They built a model called "the Hopeless Diamond" because it looked like a squat diamond and looked too hopeless to ever fly. This work marked a substantial change from the past, because for the first time, designers realized that it might be possible to make an aircraft that was virtually invisible to radar. At the conclusion of Phase 1, both contractors had achieved objectives.

Following the results of the "Pole Off," Lockheed won the sole Phase 2 award, and the Tactical Air Command became the key logistical and operations point of contact for the Air Force side of the program. Dr. William Perry, who had taken over for Currie, asked the Air Force Tactical Air Command for input. Gen. Bob Dixon and Gen. Larry Welch, based on their experience with the Skunk Works on high-risk, high classification projects, gave positive feedback. Lockheed was awarded the contract to build two subscale demonstrator aircraft (about 50 percent of the size of an operational airplane). Lead responsibility for the program was transitioned from DARPA to the U.S. Air Force Special Projects Office, and the program became known as HAVE BLUE.

However, DARPA wanted to preserve the expertise that Northrop had developed. It encouraged Northrop to maintain its team, which shortly thereafter engaged in DARPA-sponsored design studies for the Battlefield Surveillance Aircraft, Experimental (BSAX) program. These studies led to the TACIT BLUE program, which, in turn, provided data and technology for the B-2 stealth bomber program, as well as advanced cruise missiles.

The Phase 2 program - HAVE BLUE - began in 1976. HAVE BLUE was a proof-of-concept aircraft designed to test out Lockheed's concepts for "very low observable" capabilities while meeting a set of realistic operational requirements. Phase 2 was conducted as a classified, Special Access Program managed by a special office within Air Force Systems Command and utilizing special oversight procedures for congressional review. Nonetheless, Lockheed's Skunk Works managed the program in an environment open to experimentation and flexible problem solving, with a high degree of communication among scientists, developers, managers, and users. OSD leadership kept the program focused and moving forward - Phase 2 was deliberately limited to demonstrating that the RCS objectives could be achieved - in the face of many fundamental uncertainties.

Under HAVE BLUE, Lockheed built two manned technology demonstrators to validate Lockheed's pole model results. They were kept as small and simple as possible to minimize cost. There was no mission equipment, the cockpit was unpressurized, and the aircraft had no air-to-air refueling capability. Only the second aircraft had radar absorbing material (RAM) coatings. HAVE BLUE was approximately one-quarter scale [in weight] to the eventual F-117A: 38 feet long [versus 66 feet], 22.5-foot wingspan [versus 43 feet], 12,500-pound maximum take off weight [versus 52,000 pounds], 2,850-pound thrust in each of two engines, compared with the F-117A at 66 feet long, 43-foot wingspan, 52,500 pound, and 10,800 pounds of thrust per engine.

Even though these test vehicles made use of conventional off-the-shelf components and subsystems, they were truly revolutionary. Their shaping and materials were so important that their impact on aircraft survivability changed the way the U.S. Air Force fights. Technologies nurtured by DARPA included RCS reduction, RAM development, infrared shielding, reduced visual signatures, low-probability-of-intercept radar, inlet shielding, exhaust cooling and shaping, and other signature reduction disciplines.

The cross section of the vertical stabilizers was of generally diamond shape. The inward tilt of the stabilizers was considered to minimize radar cross section, since this configuration tends to hide, or mask, other elements. The angles of the tail surfaces, with an inward tilt therebetween, enhance the ability of the vehicle to display a minimum radar cross section while retaining the ability to function with reasonable aerodynamic efficiency.

Movably affixed to the respective trailing edges or the wings were elevons for vehicle control. Similarly attached for movement to the trailing regions of the vertical stabilizers were a pair of rudders for vehicle control. On the sides of the fuselage were a pair of air inlet cowlings for the aircraft propulsion system, having in their respective inlets a pair of inlet grids. The nose of the vehicle was pointed to the maximum practical extent. The leading edges were common to both the fuselage and the respective wings. The edges were made as sharp as can be accommodated structurally, as were each of the other external edges on the vehicle.

The complete outward facing surface area of the vehicle, and each of its identified components, was characterized as being faceted. For example, the upper portion of the nose section comprised three flat surfaces, namely, side surfaces and top surface. Similarly, the wing included a multiplicity of facets upon its upper surface, namely, a leading facet, an inner facet, a top facet and an end facet. The rearward portion of the fuselage included side facets and an upper rearward facet connecting them. The windshield was also constructed from a plurality of faceted segments.

The inlet cowlings had side panels angled inward and rearward, with the upper panels thereof coincident with upper rearward facet which terminates at a point at the rear of the vehicle. Since it is desirable that the vehicle incorporate air inlets of highly canted configuration, a particular operational difficulty is encountered, i.e., the ability to capture a significant amount of air in a sharply canted engine air inlet. Grids capable of providing a high percentage of air capture, i.e., directing the air into the inlets rather than permitting it to bypass those inlets as would be normal in configuration of this character. Such inlet grids also possess the desirable feature of having a low radar cross section.

The underside of the vehicle was similarly constructed of a plurality of facets, the primary ones of which were the wing and fuselage facets. A bottom rearward facet was connected to facets oriented at a discrete angle with respect to each of the others. The presence of a minimum number of large facets on the bottom surface of the vehicle greatly enhanced the low radar cross section of the vehicle. The exhaust port of the vehicle was shielded by a facet from radar and infrared detection by the extension of facets.

Since the radar cross section normal to each edge is relatively high, it was desirable that the vehicle be designed with as few edges as possible. It was also desirable that those edges which are included be oriented, to place higher cross section values into sectors where minimum radar cross section is not required. Although it is not considered possible to totally eliminate the radar cross section of a flyable vehicle, it was possible with the vehicle of this configuration to so reduce or disguise its detectability that the cross section vulnerability to detection is insignificant.

Designers wondered if it would fly. One Lockheed document stated that the "airframe exhibits just about every mode of unstable behavior possible for an aircraft-the only thing it doesn't do is tip back on its tail when it is parked." Have Blue was not inherently stable in flight and would tumble out of control. But fortunately, computers also rendered this fact irrelevant, because aircraft designers for several years had been designing planes, like the F-16 fighter, that were kept stable by computers that constantly adjusted their flight controls in the same way that a person riding a bike is constantly making minute corrections to remain balanced. This same solution was applied to the Have Blue airplane.

The first flight test in April 1977 was 20 months following contract award, and both aircraft were tested extensively. Subsequent test flights clearly demonstrated that such planes could attain the very low RCS and perform within the posited specifications. Eventually both were lost during flight test mishaps, but neither aircraft accident was related to the VLO design, and the results were clear. While both aircraft were lost in crashes during the demonstration program - when HAVE BLUE 2 was lost, only two or three planned sorties remained to be flown - they had succeeded in the proof-of-concept of a stealthy aircraft. Concurrent with demonstration that an extremely low RCS was achievable, the Air Force Systems Command conducted studies and demonstrations of the additional technologies that would be needed for such an aircraft to be a mission-capable system. (A 1977-1979 demonstration of a passive infrared fire control system was particularly critical.)

Based on these results, and guided by the high priority of countering Soviet numerical superiority with US technology, as outlined in the Offset Strategy, USD(R&E) Perry sought an accelerated development of a real weapons system. Studies were conducted of alternative concepts for employing a full-scale version of such an aircraft - as a fighter, a bomber, or a surveillance-reconnaissance system. While there were advocates for all these alternatives, its employment as a penetration-fighter was selected as the first development effort. Secretary of Defense Brown agreed to make the development of stealth aircraft "technology limited" as opposed to funding limited.



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